Methods of driving a scanning beam device to achieve high frame rates

ABSTRACT

The present invention provides methods and systems for scanning an illumination spot over a target area. The present invention removes stored energy from a scanning element to stop the scanning element from vibrating and to substantially return the scanning element to its starting position so as to enable high frame rates.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 11/833,831 (Attorney Docket No. 016336-004920US),filed Aug. 3, 2007, which is a continuation of U.S. patent applicationSer. No. 11/612,888 (Attorney Docket No. 016336-004910US), filed Dec.19, 2006, which is a continuation of U.S. patent application Ser. No.11/021,981 (Attorney Docket No. 016336-004900US/2341-4126P.1US), filedDec. 23, 2004, the full disclosures of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates generally to methods and scanning beamsystems that provide high frame rates. More particularly, the presentinvention provides methods and systems for removing energy that isstored in a resonant scanning element.

A scanning beam device that has been developed by the University ofWashington uses a single optical fiber to scan an illumination spot overa target area in a one or two dimensional scan pattern. Light reflectedfrom the target area is sequentially captured by a light detector, suchas a photodetector. The photodetector response is then used to determinethe brightness of the small portion of the image that corresponds to thesmall area illuminated by the illumination spot at that given point intime during the scanning pattern.

While the optical fiber can be driven at any number of frequencies andin any number of one or two dimensional scan patterns, the optical fiberand the illumination spot is typically driven in at resonant frequencyof the optical fiber in a spiral shaped scan pattern. “Resonant” is usedherein to mean that the optical fiber is driven within a Q-factor of itsresonant frequency. When driven within the Q-factor of the resonantfrequency (FIG. 3), the optical fiber can achieve its desired deflectionwhile using a minimal amount of energy.

As shown in FIG. 1, in an idealized spiral scan pattern 11 theillumination spot typically starts at an initial, central position andspirals outward until a maximum desired diameter is reached. Once theillumination spot reaches its maximum diameter, it is desirable toreturn the illumination spot to the center. One proposed spiral scanpattern spirals the illumination spot outward to its maximum diameter,and then spirals the illumination sport inward by retracing the originalspiral pattern. Of course, if desired, it may be possible to start thescan pattern at its maximum diameter and then spiral the illuminationspot inward toward the middle.

To achieve the resonant spiral scan pattern 11 of FIG. 1, the opticalfiber is driven along two drive axes (y and z or horizontal andvertical) with horizontal and vertical triangle amplitude modulated sinewaves 13, 15 that are driven with a 90 degree phase shift between them(FIG. 2). If the optical fiber is circular, the horizontal and verticalresonant vibrations will have the same frequency and equal amplitude(but still 90 degrees out of phase). An increasing amplitude portion 17of the drive signals 13, 15 cause the illumination spot to spiraloutward from the initial, central position. The decreasing amplitudeportion 19 of the drive signals 13, 15 cause the illumination spot tospiral inward, back toward the initial, central position. It wascontemplated that images of the target area could be obtained bycollecting back scattered light during the increasing amplitude portion17, the decreasing amplitude portion 19, or both.

Applicants have found that there are two significant issues when drivinga scanning element using the drive signals 13, 15 of FIG. 2.

First, because the scanning element is typically driven substantially inresonance, the scanning element tends to store a large amount of energy.The stored energy will cause the scanning element to continue to move atlarge amplitudes even after the amplitude of the drive signal is reduced(or removed). For example, in experiments Applicants have found that theillumination spot will follow the increasing amplitude portion 17 of thedrive signal rather closely, but when the drive signal moves to thedecreasing amplitude portion 19, the illumination spot does not followas closely. Instead, the stored energy in the scanning element causesthe illumination spot to decrease its scan diameter at a much lower ratethan the drive signal.

While image and drive remapping methods (described in commonly owned andcopending U.S. patent application Ser. No. 10/956,241, filed Oct. 1,2004, the complete disclosure of which is incorporated herein byreference) can correct for the distortions in the image caused by thedifferences between the theoretical position of the illumination spotdefined by the drive signal and the slower, actual position of theillumination spot, the stored energy in the resonating fiber may alsocause a “hole” to appear in the center of the image (FIG. 4). Remappingmethods can not correct for the hole in the center of the image. Thehole in the center of the image is caused when the drive signal repeatsthe increasing amplitude portion of the drive signal before theillumination spot can return back to the center of the image (e.g., itsinitial, center position). In some scenarios, a diameter of the hole maybe equal to half of the image, or more.

The second issue also involves the fact that the scan pattern may varyduring the increasing amplitude portions and decreasing amplitudeportions 17, 19 of the scan pattern 11. Using image or drive remappingand other techniques, however, it is possible to generate images in bothscan directions that appear identical. Unfortunately, the actual scanpattern of the illumination spot may change depending on theenvironmental factors at the site of its use. Typically, temperature hasthe biggest effect on the scan pattern. For example, on the increasingamplitude portion 17, the changes caused by the higher or lowertemperatures may be small and can be ignored or otherwise compensatedfor with the remapping methods. But for the decreasing amplitude portion19, the changes caused by the temperature may be harder to correct. Thetemperature factors may cause images in the two scan directions tochange in opposite ways. For example, on the increasing amplitudeportion, the image may rotate clockwise, while during the decreasingamplitude portion the image may rotate counter-clockwise. If images arecaptured during both the increasing and decreasing amplitude portions,this may result in a display in which two diverging images are toggledat the frame update rate, which will cause the resultant captured imageto become useless.

Therefore, what are needed are methods and systems which can providehigh frame rates while accurately generating an image of the targetarea. It would be desirable if such methods and system can compensatefor the energy stored in the resonating scanning element.

BRIEF SUMMARY OF THE INVENTION

The present invention provides methods and systems for improving a framerate of a resonant scanning beam device. More specifically, the methodsand systems of the present invention are directed at rapidly removingthe stored energy and stopping the scanning of the scanning element in ashort amount of time.

The methods of the present invention will typically provide a frame ratebetween about 5 Hz and about 60 Hz, and preferably between about 15 Hzand about 30 Hz. As can be appreciated, the present invention mayprovide frame rates below or above the aforementioned ranges, and thepresent invention is not limited to such ranges.

The methods of the present invention are applicable to bothone-dimensional and two-dimensional scan patterns. The drive signals forachieving the scan pattern may have similar frequencies in both ahorizontal drive axis and a vertical drive axis (e.g., for a spiral scanpattern) or the scan pattern may have different frequencies in thehorizontal drive axis and vertical drive axis (e.g., for a propellerscan, raster scan, or the like).

For improved stability and scan repeatability over various environmentalconditions, images of the target area are typically only captured duringone portion of the drive signal. For example, in a spiral scan pattern,image data is captured only during a first portion of the scan patternin which an illumination spot is spiraled outward from an initial,center position. A second portion of the scan pattern is used to returnthe illumination spot to its initial center position. Once theillumination spot returns to the center position, the drive signal canbe repeated.

In one aspect, the present invention is directed toward generating andapplying a drive signal for the second portion of the scan pattern thatis configured to return the illumination spot as rapidly as possiblefrom the end of the first portion of the scan pattern to the initialcenter point. Reducing the retracing time will allow for an increasednumber of spiral scans that are devoted to image acquisition.

In one embodiment, the drive signal used to drive the scanning elementcomprises a first component and a second component. The first componentof the drive signal will be used to scan the illumination spot over thetarget area in the desired scan pattern. The second component of thedrive signal will be used to remove stored energy from the scanningelement. In one configuration, the second component of the drive signalis a phase braking signal that is phase shifted from the first componentof the drive signal. The second component of the drive signal rapidlyremoves the energy from the scanning element so as to return thescanning element substantially to its zero motion point. Because thescanning element is typically brought to rest at its center point, animage of the target site without holes may be generated.

When the scanning element is driven at resonance, the drive signal andthe position of the illumination spot are approximately 180 degrees outof phase. To remove the energy stored in a resonant system, the phasebraking signal (e.g., the second component of the drive signal) isforced in phase with the position of the illumination spot. This isaccomplished by changing the phase of the horizontal and vertical drivesignals from the first component by approximately 180 degrees. This isequivalent to inverting both the Y and Z drive signals.

However, if the phase of the drive signal is kept constant throughoutthe second component, the changing phase of the position of the scanningelement will eventually reach the point where the fiber is drivenapproximately 90 degrees out of phase and the amplitude will begin toincrease. In fact, Applicants have found that anything other thanin-phase driving reduces the rate at which energy is removed from thesystem. For this reason it is desirable to continually adjust the phaseof the drive signal such that it remains in phase with the position ofthe scanning element until substantially all of the energy is removedand motion of the scanning element substantially stops. As soon assubstantially all of the energy is removed from the scanning element andthe scanning element is substantially motionless, the drive signal willreenergize the scanning element and the scan amplitude will increase.

One exemplary method of determining an appropriate phase braking drivesignal or second component of the drive signal is to use a feedbackcontrol loop. The feedback control loop (whether real-time or iterative)can be used to determine the appropriate drive signal to quickly removethe energy from the scanning element. The generated drive signal can berecorded in a memory of the system and used as the second component ofthe drive signal. In alternative embodiments, an operator may manuallyadjust the phase of the drive signal until all or substantially all ofthe energy is removed from the scanning element.

In additional aspects, the present invention is directed toward methodsand systems for generating and applying a drive signal to a scanningbeam device so that the scanning element is caused to scan anillumination spot over a target and then returned to a starting positionby using the drive signal to remove kinetic energy from the scanningelement. During the period where energy is being removed, a frequency ofthe drive signal can be selected to match a natural frequency of thescanning element.

Other aspects, objects and advantages of the invention will be apparentfrom the detailed description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary two-dimensional scan pattern that isencompassed by the present invention.

FIG. 2 illustrates one exemplary y-axis drive signal and z-axis drivesignal that may be used to generate the scan pattern of FIG. 1.

FIG. 3 illustrates a Q-factor of a resonant frequency.

FIG. 4 illustrates an image of a target area that has a hole in acenter.

FIG. 5 shows one example of a y-axis drive signal envelope that scansthe scanning element in a two dimensional spiral pattern and removesenergy from the scanning element to return the scanning element to itsstarting position.

FIG. 6 shows a 90 degree offset between the y-axis drive signal and thez-axis drive signal in a first component of the drive signal.

FIG. 7 shows an inverted y-axis drive signal and the z-axis drive signal(compared to FIG. 6) that forms part of the second component of thedrive signal.

FIG. 8 shows another example of a y-axis drive signal envelope that isencompassed by the present invention.

FIG. 9 schematically illustrates a scanning beam system encompassed bythe present invention.

FIG. 10 illustrates a simplified scanning fiber system encompassed bythe present invention.

FIG. 11 schematically illustrates a kit encompassed by the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides methods and systems for improving a frameupdate rate of a scanning beam device by rapidly removing stored energyin a scanning element and returning the scanning element to its startingposition.

The scanning beam systems of the present invention include a scanningbeam device and a base station for controlling the image formation orimage acquisition of the scanning beam device. The scanning beam devicesof the present invention may take on a variety of forms, but aretypically in the form of an endoscope, catheter, fiberscope, microscope,boroscope, bar code reader, an image display, or other devices forgenerating images or acquiring images of a target area. The scanningbeam devices of the present invention may be a limited use device (e.g.,disposable device) or a multiple-use device. If the device is formedical use, the scanning beam devices will generally be sterile, eitherbeing sterilizable or being provided in hermetically sealed package foruse.

The scanning beam devices of the present invention include a scanningelement for scanning a beam of light onto a target area. The scanningelement preferably comprises a single, cantilevered optical fiber. Inother embodiments, the scanning element may take the form of mirrors,such as microelectomechanical system (MEMS), galvanometer, a polygon,multiple optical elements moved relative to each other, or the like.While the remaining discussion focuses on scanning fiber device that isused for acquiring images of a target site, it will be appreciated thatthe present invention also encompasses the other aforementioned scanningelements and systems.

The methods of the present invention focus on the use of atwo-dimensional spiral scan. It should be appreciated however, that thepresent invention is not limited to such a scan pattern. For example,the present invention may also use other two dimensional scan patternssuch as a rotating propeller scan pattern, a raster scan pattern, or aone-dimensional line pattern.

FIGS. 5 and 8 schematically illustrate two scan envelopes 23 thatillustrate some examples of possible amplitudes changes of the drivesignal over a single cycle of the scan pattern. For ease of reference,only a drive envelope for the Y-axis drive signal are shown in FIGS. 5and 8. It should be appreciated however, that for a spiral scan patternof a round optical fiber, the scan pattern for the y-axis drive signaland the z-axis drive signal will generally have a similar shapedenvelope, and the primary difference between the two drive signals 13,15 (FIG. 2) will be a phase offset of the y-axis and z-axis drivesignals within the drive envelope.

The drive signal comprises a first component 27 and a second component29. An ideal first component 27 of the drive signal will comprise asinewave that has a linearly increasing amplitude (e.g., the increasingamplitude portion 17). However, drive remapping of the drive signal maychange the envelope of the first component of the drive signal and theenvelope may not have a linearly increasing amplitude.

At the end of first component 27, the illumination spot will havereached the largest diameter of the scan pattern (FIG. 1). After theillumination spot has reached its largest diameter, it is desirable toreturn the illumination spot and scanning element back to its initialstarting point (e.g., the center of the spiral).

Because of the aforementioned differences of the scan pattern of theillumination spot during the increasing amplitude portion 17 (e.g., thefirst component 27) and the decreasing amplitude portion 19 of the drivesignal (e.g., the second component 29; FIG. 2), data acquisition (e.g.,imaging of the target area) will typically occur during only one of thefirst component 27 of the drive signal and the second component 29 ofthe drive signal. In a preferred embodiment, imaging of the target areawill occur during the spiraling of the illumination spot outward, and noimaging of the target area will occur as the illumination spot isreturned substantially to “zero” (e.g., at or near its initial, centerposition).

Applicants have found that if the drive signal is simply set to “zero,”the motion of the illumination spot will exponentially decay towardzero. Unfortunately, the exponential decay takes a considerable amountof time that is not conducive to high frame rates. For example,Applicants found that for a scan pattern that has 250 increasingspirals, it would take over 600 spiral periods for the motion of theillumination spot to settle to zero and return to the initial, centerpoint. However, instead of simply decreasing an amplitude of thesinewave, the present invention applies a “phase braking” secondcomponent 29 of the drive signal whose signal has a phase shift relativeto the drive signal in the first component 27. In a preferredembodiment, the second component 29 has an inverted phase relative tothe first component 27.

When the scanning element is scanned at its resonant frequency, thedrive signal and the position of the illumination spot are approximately180 degrees out of phase. To remove the energy stored in the resonatingscanning element, the second component 29 of the drive signal is forcedinto phase with the position of the scanning element. FIG. 6schematically illustrates y-axis and z-axis drive signals that are usedto drive the scanning element during a first component 27 of the drivesignal. As shown in FIG. 6, the y-axis drive signal and the z-axis drivesignal are 90 out of phase.

In a preferred method shown in FIG. 7, the second component 29 of thedrive signal is forced into phase with the position of the scanningelement by changing the phase of the y-axis drive signal and the z-axisdrive signal by approximately 180 degrees. Forcing the y-axis and z-axisdrive signal into phase with the position of the illumination spot isequivalent to inverting the y-axis and z-axis drive signals.

The phase braking signal typically has the effect of rapidly reducingthe amplitude of the scanning element motion and slightly slowing thefrequency of the scanning element. The slowing frequency of the scanningelement, however, causes the phase relationship between the drive signaland the position of the scanning element (and illumination spot) tochange over time. Applicants have found that it is highly desirable tomaintain the second component 29 of the drive signal in phase with theposition of the scanning element substantially throughout the secondcomponent of the signal. If the phase of the second component of thedrive signal is kept constant, the changing frequency and changingposition of the scanning element will inevitably reach a point where thescanning element is again 180 degrees out of phase with the signal. Whenthe second component 29 of the drive signal and the position of thescanning element are approximately 90 degrees out of phase with eachother, the amplitude of the movement of the scanning element will againbegin to increase and energy will again be stored in the scanningelement, instead of being removed.

In order to remove the energy from the scanning element, it is desirableto continually adjust the phase of the drive signal so that the drivesignal remains in phase with the scanning element until most or all ofthe energy is removed from the scanning element and the scanning elementmovement is substantially stopped. Once the energy is removed from thescanning element and the scanning element is positioned substantiallyback at its initial starting point (e.g., at or near the center ofspiral, at or near the center of range of motion, and/or at or near thecenter of the target area), the drive signal cycle may be repeated andthe increasing amplitude first component 27 of the drive signal mayagain cause the illumination spot to spiral outward in its imagingpattern.

In addition to the phase shift, the drive signal envelope shape of thesecond component 29 may be optimized to rapidly remove the stored energyfrom the scanning element and substantially return the scanning elementback to zero. Using the phase shifted second component 29 of the drivesignal and modified drive signal envelopes described herein, Applicantshave been able to remove the stored energy from the scanning element inless than about 50 spiral periods.

FIGS. 5 and 8 illustrate some examples of drive envelopes that may beused as a phase braking driver to remove energy from the scanningelement. As shown in FIG. 5, the imaging portion comprises the firstcomponent 27 of the drive signal that has the increasing amplitude thatextends from sample points 0 to 25000. At sample point 25000, thescanning element reaches its largest desired diameter and the secondcomponent 29 of the drive signal is used to remove energy from thescanning element. Thus, at sample point 25000, the phase of both they-axis and z-axis drive signals are reversed. While not shown in FIG. 5,it should be appreciated that the phase of the second component 29 ofthe drive signal may be continually adjusted so as to maintain the inphase relationship with the position of the illumination spot.

In addition to changing the phase of the drive signal, the amplitude ofthe drive signal may also be adjusted during the second component 29 ofthe signal. In the illustrated example, the amplitude of the drivesignal is held constant for a number of sample points (from samplepoints 25000 to 28000) to quickly remove energy from the scanningelement. At sample point 28000, after a majority of the energy has beenremoved the amplitude of the signal is reduced so as to not re-energizethe scanning element. Finally, for a small number of sample points (fromsample point 29500 to 30000) the drive signal is set to zero to allowthe scanning element motion to substantially settle to zero.

FIG. 8 shows another example of a drive envelope that may be used toremove energy from the scanning element. As shown in FIG. 8 the imagingportion comprises the first component 27 of the drive signal that has asubstantially linearly increasing amplitude that extends from samplepoints 0 to 25000. Similar to FIG. 5, at sample point 25000, thescanning element reaches its largest desired diameter and the secondcomponent 29 of the drive signal is used to remove energy from thescanning element. Thus, at sample point 25000, the phase of both they-axis and z-axis drive signals are reversed. Instead of changing theamplitude of the drive signal, the amplitude is kept constant fromsample points 25000 to 29000. At sample point 29000, the drive signal isset to zero to allow the scanning element to substantially settle tozero (e.g., from points 29000 to 30000).

As can be appreciated, the drive envelopes shown in FIGS. 5 and 8 aremerely two examples of drive envelopes that may be used to remove energyfrom the scanning elements of the present invention. The secondcomponent 27 may have any combination of a linear or non-linearincreasing amplitude, exponentially increasing or decreasing amplitude,a linear or non-linear decreasing amplitude, and/or a zero amplitude,and the amplitudes of the second component 29 of the drive signal willvary according to the specific scanning element and imaging conditions.

Continuous adjusting of the phase to keep the position of the scanningelement and the drive signal in phase causes a small change in thefrequency of the drive signal. Thus, because phase and frequency arerelated to each other, instead of adjusting the phase of the drivesignal it may be possible to instead adjust a frequency of the drivesignal to achieve a similar removal of energy from the scanning element.In such embodiments, it may be desirable to continually adjust thefrequency of the drive signal throughout the second component 29 of thedrive signal until substantially all of the stored energy is removedfrom the scanning element.

In configurations in which the drive assembly for the scanning elementis a piezoelectric drive assembly, the controller typically generates avoltage drive signal. In such configurations, a polarity of the voltageof the drive signal is changed during the second component 29 of thedrive signal to remove energy from the scanning element. If desired,after the voltage polarity is adjusted, the voltage level may beincreased to remove the stored energy from the scanning element morerapidly. As can be appreciated, the concepts of the present inventioncan be used for any types of drive signal (e.g., current signal) and anytype of drive assembly, and the present invention is not limited to avoltage drive signal.

Because different scanning elements and drive assemblies will havedifferent characteristics, in order to properly operate the scanningbeam system, a customized drive signal for the scanning beam systemshould be used. The customized drive signal may scan the scanningelement at its resonant frequency and may provide an improved scan rateby driving the scanning element with a drive signal that quicklyrepositions the scanning element back at its zero position after eachscan cycle of the target area.

The customized drive signal may be generated using any conventionalmethod, but will typically be generated by manually adjusting the phaseof the second component of the drive signal or by using one or morefeedback control loops during calibration. The feedback control loopsmay be real-time or iterative. In one embodiment, a feedback controlloop may be used by the manufacturer prior to packaging of the scanningbeam device. The feedback control loop may optionally be used to remapan ideal first component of the drive signal so that the illuminationspot will follow the ideal scan pattern. Thereafter, the same ordifferent feedback control loop may be used to determine the secondcomponent of the drive signal that rapidly removes the energy from thescanning element and moves the scanning element back to zero.Thereafter, the customized drive signal may be stored in a memory in thescanning beam device as an algorithm or look up table.

When the scanning beam device is coupled to a controller, the controllermay download the customized drive signal of the particular scanning beamdevice from the memory. A more complete description of a memory andother data that may be stored on the memory of the scanning beam deviceis described in commonly owned and copending U.S. patent applicationSer. No. 10/956,473, filed Oct. 1, 2004, entitled “Configuration Memoryfor a Scanning Beam Device”, the complete disclosure of which isincorporated herein by reference.

In other configurations, the drive signal may be determined at theimaging site by the operator by calibrating the particular scanning beamelement just prior to imaging the target area. For example, the scanningbeam element may be placed in a calibration chamber that is coupled toor formed in the base station, and the drive signal may be manually orautomatically remapped and calibrated to determine an appropriate firstcomponent 27 and second component 29 of the drive signal. Once the drivesignal is determined for that specific scanning beam device, the drivesignal may be stored as an algorithm or table in a memory of thescanning beam device. Of course, in other embodiments, the customizeddrive signal may be stored in other computer readable storage elementsbeside the memory in the scanning beam device. For example, thecustomized drive signal may be stored in a memory of the controller, aremote database that is accessible by the controller or the like.

FIGS. 9 and 10 illustrate scanning beam systems 10 that are encompassedby the present invention. The scanning beam system 10 may include a basestation 12 and a scanning beam device 14. The scanning beam device 14includes a connector member 16 that is configured to mate with an inputinterface 18 on the base station. Coupling of the connector member 16 tothe input interface 18 may create a power path, drive signal path,detector path, illumination path, and/or data communication path betweenelements of the base station 12 and related elements of the scanningbeam device 14.

As shown in FIG. 9, base station 12 typically includes a controller 20that has one or more microprocessors and/or one or more dedicatedelectronics circuits which may include a gate array (not shown) whichmay control the actuation of the scanning beam device 14 and generationof the images. The controller 20 may also include scanner driveelectronics, detector amplifiers and A/D converters (not shown). Thedrive electronics in the controller and the software modules stored inmemory are used to provide a customized control routine for the scanningbeam device 14. The methods of the present invention may be implementedwith hardware, software, firmware, specialized circuitry, specializedprocessors, or a combination thereof. In embodiments, in which themethods are carried out as software, the software is preferablyimplemented as an application program in the form of a plurality ofsoftware modules that are tangibly embodied in a memory of the system oron other computer readable medium. While the remaining discussionfocuses on a software implementation of the methods of the presentinvention, it should be appreciated that the present invention is notlimited to the software implementation.

Controller 20 is in communication with a plurality of elements withinthe base station 12 via a communication bus (not shown). Thecommunication bus typically allows for electrical communication betweencontroller 20, a power source 22, memory 24, user interface(s) 26, oneor more light sources 28, one or more output displays 30, and aphotosensitive position sensor 82. Optionally, if the scanning beamdevice 14 includes a detection assembly, the base station 12 may includea separate image storage device 32 in communication with controller 20.In alternative embodiments, the image storage device 32 may simply be amodule within memory 24. As can be appreciated, the base stations 12 ofthe present invention will vary, and may include fewer or more elementsthan illustrated in FIG. 9.

Depending on the particular scanning beam device 14 used, the lightsource 28 may emit a continuous stream of light, modulated light, or astream of light pulses. Base station 12 may comprise a plurality ofdifferent light sources 28 so as to be able to operate differentscanning beam devices that have different illumination capabilities. Thelight sources 28 may include one or more of a red light source, bluelight source, green light source (collectively referred to herein as a“RGB light source”), an IR light source, a UV light source, and/or ahigh intensity laser source (typically for a therapeutic scanning beamdevice). The light sources 28 themselves may be configured to beswitchable between a first mode (e.g., continuous stream) and a secondmode (e.g., stream of light pulses). For ease of reference, otherconventional elements in the light source are not shown. For example, ifa RGB light source is used, the light sources may include a combiner tocombine the different light before it enters the optical fiber 50.Furthermore, while light source 28 is illustrated in FIG. 10 as beingseparate from base station 12, it should be appreciated that in otherembodiments, light sources 28 may be integrated within base station 12.

Memory 24 may be used for storing the software modules that carry outthe methods of the present invention, look-up tables, and algorithmsthat control the operation and calibration of the scanning beam device14. The control routine used by the controller 20 for controlling thescanning beam device 14 will typically be configurable so as to matchthe operating parameters of the attached device (e.g., resonantfrequency, voltage limits, zoom capability, color capability, etc.). Asnoted below, memory 24 may also be used for storing the image datareceived from the detectors 46 of the scanning beam device, imageremapping look-up tables and algorithms, remapped drive signals thatcomprise the first component 27 and second component 29, parameters ofthe fiber scanning device, etc.

For ease of reference, other conventional elements in the base station12 are not shown. For example, embodiments of the base stations 12 ofthe present invention will typically include conventional elements suchas amplifiers, D/A converters and A/D converters, clocks, waveformgenerators, and the like.

The scanning beam devices 14 of the present invention includes ascanning element 34 for delivering and scanning a beam of light onto atarget area 36. A waveguide 38, typically in the form of an opticalfiber, is optically coupled to the light source(s) so as to deliverillumination from the light source 28 to the scanning element 34. Adriving assembly 40 is coupled to the scanning element 34 and is adaptedto actuate the scanning element 34 according to a drive signal receivedfrom the controller 20. Optionally, the scanning beam device 14 mayinclude a non-volatile memory 39 for storing identification data orparametric data of the scanning beam device 14.

In a preferred embodiment, the scanning element 34 is a cantileveredoptical fiber 50. The optical fiber 50 will comprise a proximal portion52 and a distal portion 54 that comprises a distal tip 56. Optical fiber50 is typically fixed along at least one point of the optical fiber soas to be cantilevered such that the distal portion 54 is free to bedeflected. In such an embodiment, the proximal portion 52 of the opticalfiber is the waveguide 38 and will transmit light from light source 28.As can be appreciated, in other embodiments, a separate waveguide 38 maybe optically coupled to the proximal portion 52 of the optical fiber sothat light from light source 28 will be directed into the optical fiber50 and out of the distal tip 56.

The optical fiber 50 may have any desired dimensions and cross-sectionalshape. The optical fiber 50 may have a symmetrical cross sectionalprofile or an asymmetrical cross-sectional profile, depending on thedesired characteristics of the device. An optical fiber 50 with a roundcross-section will have substantially the same resonance characteristicsabout any two orthogonal axes, while an optical fiber with an asymmetriccross section (e.g., ellipse) will have different resonant frequenciesabout the major and minor axes. If desired, the optical fiber 50 may belinearly or non-linearly tapered.

To achieve the deflection of the distal portion 54 of the optical fiber,the cantilevered distal portion 54 of the optical fiber 50 will becoupled to drive assembly 40. As shown in FIG. 3, drive assembly 40 willtypically drive the cantilevered distal portion 54 within a Q-factor ofthe resonant frequency, and preferably at its mechanical or vibratoryresonant frequency (or harmonics of the resonant frequency) in a one ortwo dimensional scan pattern. As can be appreciated, the scanningelement 34 does not have to be driven at substantially the resonantfrequency, but if the scanning element 34 is not scanned at its resonantfrequency, a larger amount of energy will be required to provide thedesired radial displacement for the scan pattern. In one preferredembodiment, the drive assembly is a piezoelectric driving assembly. Adrive signal from controller 20 delivers a desired signal to the driveassembly 40. The drive signal causes the piezoelectric drive assembly todeflect the distal tip 56 of the optical fiber 50 so that theillumination spot is moved in a desired scan pattern. While preferreddrive assemblies are piezoelectric assemblies, in alternativeembodiments, the drive assembly 40 may comprise a permanent magnet, aelectromagnet, an electrostatic drive, a sonic drive, anelectromechanical drive, or the like.

Referring again to FIG. 10, the scanning beam device 14 may optionallycomprise one or more lenses 58 near the distal end of the optical fiber50 to focus the imaging light, to provide better resolution, and/or animproved FOV. The lenses 58 may be coupled to an outer housing (notshown) of the scanning fiber device 14 and fixed relative to thescanning distal end 56 of the optical fiber and/or the lens 58 may bemovable relative to the housing (not shown).

A detection assembly 44 may comprise one or more detectors that are incommunication with the controller. The detectors are typically coupledto the controller through an amplifier and A/D converter (not shown).The controller (or drive electronics within the controller) may providea synchronization pulse to provide a timing signal for the dataacquisition by the detection assembly 44. Additionally or alternatively,a separate clock circuit (not shown) may be used to correspond thedetected light to the time points in the scan pattern. The detectionassembly 44 may be disposed anywhere on or within the housing of thescanning fiber device, but will typically be positioned adjacent thedistal portion 54 of optical fiber 50 so as to capture backscatteredlight reflected off of the target area 36. The detection assembly 44 maycomprise one of more individual detectors to receive light backscatteredfrom the target area 36. For example, the detection assembly maycomprise a light detector (such as a photodetector) that produceselectrical signal that are conveyed through leads (not shown) to thebase station 12. Alternatively, the detection assembly 44 may compriseone or more collector fibers (not shown) that transmit light reflectedfrom the target area to photodetectors in the base station 12.

The calibration methods for determining the first and second componentof the drive signal may be carried out in a calibration chamber 80 shownschematically in FIG. 9. Calibration chamber 80 may be formed as part ofthe base station 12, it may be separate from the base station 12, or itmay be incorporated as part of the manufacturer's test equipment (notshown). Calibration chamber 80 may be used during a calibration step to(1) determine the resonant frequency of the scanning fiber, (2) to remapthe first component of the drive signal, and (3) to determine andoptimize the second component 29 of the drive signal to remove thestored energy from the scanning fiber.

Calibration chamber 80 may be environmentally controlled so as to matchthe anticipated environments of the scanning fiber devices. Calibrationchamber 80 will be sized to receive at least a distal portion of thescanning fiber device 14 and may have a holder (not shown) thatpositions the scanning fiber device substantially in a center of thecalibration chamber 80. Calibration chamber 80 will typically have alight detector coupled to the controller. The light detector ispreferably a position sensitive detector (PSD) 82 that captures theposition of the illumination spot during the scan pattern. In use, thecontroller will be configured to initiate the scanning pattern. Analogsignals from the PSD 82 will be sent to the dedicated, specializedhardware electronics in the controller through an A/D converter (notshown) and the controller will correspond the position data with thetime points of the scan pattern. Optionally, the calibration chamber mayhave a temperature controller and a temperature sensor coupled to thecontroller. Controller may be configured to measure and/or adjust thetemperature of the calibration chamber before or after thecharacterization of the scan pattern of the scanning fiber device.

Because the characteristics of the scanning fiber device 14 may operatedifferently in different operating modes (e.g., different zoom levels,etc.) or operate differently in different environmental conditions(e.g., temperature, etc.), separate look-up tables or algorithms may begenerated when the scanning fiber device is in the calibration chamber80 for some or all of the selected operation modes and/or environmentalconditions. If only selected operation modes or environmental conditionsare used to generate a look up table, the controllers of the presentinvention may be configured to interpolate between the generated look-uptables and algorithms to generate look-up tables for other modes andconditions.

For example, in one configuration, there may be separate look-up tablefor different zoom levels. Zoom is generally accomplished by reducingthe maximum drive voltage delivered to the drive assembly 40 so as toreduce the amplitude of the scanning. However, the different voltagescould provide different positional differences other than simpleamplitude changes in the optical fiber and illumination spot. As such,it may be desirable to have different look-up tables for the differentzoom levels. The zoom capability may be limited to specific zoom levelsso that memory is not overloaded with a large number of look-up tablesor algorithms. It may be possible to provide a predetermined number oflook-up tables for a predetermined spaced zoom levels and anynon-characterized zoom level between the predetermined zoom levels mayhave a look-up table generated by the controller by interpolatingbetween the spaced zoom tables.

Additionally, there may be different first components and secondcomponents of the drive signals for the different anticipatedenvironmental conditions. For example, the memories in the system 10 maycomprise look-up tables or algorithms for a variety of differenttemperatures or temperature ranges. In such embodiments, the scanningfiber device 14 may comprise a temperature sensor (not shown) that isconfigured to measure the temperature adjacent the distal tip 56 of theoptical fiber 50 and configured to send a temperature signal to thecontroller so that the controller will know which look-up table oralgorithm to use. Similar to the zoom tables, it may be desirable toonly generate look-up tables for two or more temperatures or temperatureranges. The look-up tables for the two or more temperatures maythereafter be interpolated to generate the look-up tables for theremaining temperatures or temperature ranges.

To acquire an image of a target area 36 with the scanning fiber device14, light is delivered from light source 28 through the waveguide 38 andprojected out of the distal end 56 of the optical fiber so as to form anillumination spot 42 on the target area 36. A first component 27 of thevoltage drive signal (either the ideal signal or the remapped drivesignal) is delivered through the power source so that the piezoelectricdrive assembly 40 vibrates the optical fiber substantially at itsresonant frequency and scans the illumination spot in a two-dimensionalspiral scan pattern over the target area 36. Backscattered light fromthe target is sequentially collected by the detection assembly 44 andits collection times are synchronized with its time point in the spiralscan pattern. Based on the known position of the illumination spot atall points of the scan pattern, the sequentially collected light maythen be placed in a pixel position that corresponds to the position ofthe illumination spot at that particular time of the scan pattern toconstruct an image of the target area one pixel at a time. Once theillumination spot has reached its outer diameter, the second component29 of the drive signal is delivered to remove the stored energy from theoptical fiber and to return the optical fiber to its zero position.

Referring now to FIG. 11, the present invention also encompasses kits300. The kit 300 may include a scanning fiber device (SFD) 14 (such asan endoscope), instructions for use (IFU) 302, and at least one package304. Optionally, the kit 300 may include a computer readable medium(CRM) 306 that is integral with the SFD 14 (such as the non-volatilememory 39) or separate from the SFD (e.g., CD, DVD, floppy disk, etc.)

The scanning fiber device 14 will generally be as described above, andthe instruction for use (IFU) 302 will set forth any of the methodsdescribed above. Package 304 may be any conventional device packaging,including pouches, trays, boxes, tubes, or the like. IFU 302 willusually be printed on a separate piece of paper, but may also be printedin whole or in part on a portion of the package 304.

The scanning fiber devices may comprise a memory 39 that comprises alook-up table that provides a modified drive signal that comprises thefirst component for scanning the optical fiber over the target area andsecond component for quickly removing stored energy from the opticalfiber and/or other parametric information regarding the scanning fiberdevice. Alternatively, a separate computer readable medium 306 maycomprise the customized look-up table or algorithm for the drive signal,and/or the parametric data of the scanning fiber device.

As set forth above, the present invention can include rapidly removingthe stored energy and stopping the scanning of the scanning element in ashort amount of time by coordinating the second component of the drivesignal with the movement of the scanning element. An undriven scanningelement tends to oscillate approximately at its natural frequency, whichcan vary with oscillation amplitude. Increased levels of coordinationbetween the frequency and phase of the second component of the drivesignal and the movement of the oscillating scanning element can providefor increased energy removal rates. In order to better coordinate thesecond component with the movement of the scanning element, the secondcomponent can be changed or varied during the energy removal period tobetter match the instantaneous movement frequency of the scanningelement.

Increased coordination between the second component of the drive signaland the movement of the scanning element can be achieved using a varietyof ways. In one approach, the frequency of the second component ischosen to match a natural frequency of the scanning element. Further, tobetter match the changing movement frequency of the scanning elementthat occurs as the amplitude of oscillation changes, the frequency ofthe second component may be changed one or more times. In a furtherapproach, the frequency of the second component is continually varied soas to match the continually varying movement frequency of the scanningelement that results due to changes in its natural frequency withchanging amplitude of oscillation. Additionally, as discussed above, theamplitude of the second component may be varied in a variety of ways,for example, by changing the amplitude one or more times or evencontinually varying the amplitude. Changes to the amplitude of thesecond component may be made independent of changes to the frequency ofthe second component.

An additional feature of the present invention relates to the use ofdrive signals comprising separate components about two separate axes. Asdiscussed above, the drive signal can be comprised of a y-axis componentand a z-axis component. In the case of a spiral scan pattern of ascanning element with perfectly symmetrical vibratory characteristics,both the y-axis component and the z-axis component may be sinusoidal innature and typically 90 degrees out of phase. However, in reality, evennominally symmetrical scanning elements have some level of difference invibratory characteristics about different axes, such as slightdifferences in natural frequencies at any one particular amplitude.Further, as discussed above, scanning element natural frequency may varywith amplitude. Accordingly, it can be beneficial to account for thesedifferences in vibratory characteristics by individually tailoring they-axis and z-axis components, such that the y-axis and z-axis componentshave their own frequency profile. Such individual tailoring can involvechanging each component's frequency one or more times as discussedabove, or even continuously varying each component's frequency. At leastwhere the y-axis and z-axis components have been individually tailored,such as having different frequencies at some point in time, the phaseangle between the y-axis and z-axis components of the drive signal maybe something other than 90 degrees at any particular point in time.Additionally, as discussed above, the amplitudes of the y-axis andz-axis components respectively may be individually tailored independentfrom the tailoring of the frequencies of the y-axis and z-axiscomponents.

It is understood that the examples and embodiments described herein arefor illustrative purposes only and that various modifications or changesin light thereof will be suggested to persons skilled in the art and areto be included within the spirit and purview of this application andscope of the appended claims. For example, while the first component 27and the second component 29 of drive signal are illustrated anddescribed as different portions of a single signal, in alternativeembodiments, the first component 27 and the second component 29 can beformed of two separate signals. Moreover, while the above descriptionfocuses on image acquisition, the above systems and methods are equallyapplicable to image displays. Finally, while most embodiments of thepresent invention prefer to remove the hole from the image, it may bedesirable to not remove all of the stored energy from the scanningelement and to leave the hole in the image. Consequently, a majority,but not all, of the energy may be removed from the scanning element, andthe scanning element will only “substantially” return to itsstarting/initial point. Numerous different combinations are possible,and such combinations are considered to be part of the presentinvention.

1. A method of driving a scanning beam device that comprises a scanningelement, the method comprising: providing the scanning element in afirst position; driving the scanning element, at a frequency within aQ-factor of the scanning element's resonant frequency, with a firstcomponent of a drive signal to scan an illumination spot in a scanpattern over a target; and driving the scanning element with a secondcomponent of the drive signal to remove stored energy from the scanningelement so as to cause the scanning element to substantially return tothe first position, the second component comprising a frequency thatcorresponds to a natural frequency of the scanning element.
 2. Themethod of claim 1, wherein the second component comprises at least twodifferent frequencies.
 3. The method of claim 2, wherein the at leasttwo frequencies substantially correspond with the scanning element'smovement frequency at two or more different times during application ofthe second component.
 4. The method of claim 2, wherein the secondcomponent comprises a plurality of frequencies with each frequencysubstantially corresponding with different movement frequencies of thescanning element during energy removal.
 5. The method of claim 1,wherein the second component comprises a first-axis signal and asecond-axis signal, where at least one point in time exists where thefrequency of the first-axis signal is different than the frequency ofthe second-axis signal.
 6. A scanning beam system comprising: a scanningbeam device comprising a scanning element coupled to a drive assembly;and a base station coupleable to the drive assembly of the scanning beamdevice, the base station being adapted to deliver a drive signal to thedrive assembly to drive the scanning element, wherein the drive signalcomprises: a first component that is configured to scan an illuminationspot emitted from the scanning element from a starting position in ascan pattern and to drive the scanning element at a frequency within aQ-factor of a resonant frequency; and a second component that isconfigured to remove stored energy from the scanning element so as toreturn the scanning element to the starting position, the secondcomponent comprising a frequency corresponding to a natural frequency ofthe scanning element.
 7. The system of claim 6, wherein the secondcomponent comprises at least two different frequencies.
 8. The system ofclaim 7, wherein the at least two different frequencies substantiallycorrespond with the scanning element's movement frequency at two or moredifferent times during application of the second component.
 9. Thesystem of claim 7, wherein the second component comprises a plurality offrequencies with each frequency substantially corresponding withdifferent movement frequencies of the scanning element during energyremoval.
 10. The system of claim 6, wherein the second componentcomprises a first-axis signal and a second-axis signal, where at leastone point in time exists where the frequency of the first-axis signal isdifferent than the frequency of the second-axis signal.